#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int main() {
	char *p, *q, ch;
	p = new char[100];
	while (gets(p)) {


		int i, j;
		int n = strlen(p);
		q = new char[n];
		if (n % 2 == 0) {
			for (i = 0; i < n / 2 - 1; i++) {
				for (j = i + 1; j < n / 2; j++) {
					if (p[i] > p[j]) {
						ch = p[i];
						p[i] = p[j];
						p[j] = ch;
					}
				}
			}
			for (i = 0; i < n / 2; i++) {
				ch = p[i];
				p[i] = p[i + n / 2];
				p[i + n / 2] = ch;
			}
		} else {
			for (i = 0; i < n / 2 - 1; i++) {
				for (j = i + 1; j < n / 2; j++) {
					if (p[i] > p[j]) {
						ch = p[i];
						p[i] = p[j];
						p[j] = ch;
					}
				}
			}
			for (i = 0; i < n / 2; i++) {
				ch = p[i];
				p[i] = p[i + n / 2 + 1];
				p[i + n / 2 + 1] = ch;
			}
		}
		printf("%s\n", p);
	}

}